1. Field of the Invention
The invention relates to a method for transmitting data in a packet-oriented communication network having a guaranteed maximum transmission time for the data packets in the communication network and to a user terminal configured for participation in the communication. The communication network (also called network in brief) is, in particular, the communication network of a motor vehicle, for example a network according to the Ethernet AVB standard.
According to one embodiment of the invention, a specific quality of service as a capacity of the communication link is reserved prior to a data transmission by a reservation request from a sender of data to one or more receivers of the data. The request for quality of service as a capacity of the communication link between sender and receiver in the network is guaranteed for the datastream with a confirmation of the reservation request. Alternatively, an indication is given by a rejection of the reservation request that a data transmission is not possible.
In particular, the rejection can contain an error code such as, for example, an information “inadequate data rate”. Usually, and corresponding to the standard, this does not however contain a status message about the network and, in particular, the data rate still available in the network.
2. Description of the Prior Art
Usually, the data is forwarded in a datastream coming from the sender over further user terminals of the network, so-called switches, to the receiver(s). This also applies to the reservation request, the sender receiving a confirmation coming from the receiver when the reservation request arrives at the receiver with a positive assessment by the switches forwarding the datastream and the receiver being capable of and ready for receiving and processing the requested datastream. The receiver then actively sends out a confirmation which can be conducted back to the sender via the switches.
The rejection following a reservation request can come from the nominal receiver(s) of the datastream when they cannot or do not want to process the data. On the other hand, a rejection following the reservation request can also be effected by one of the interconnected switches provided for forwarding the data packets when it can currently not provide the requested quality of service, especially the requested data rate and latency. The reservation request can therefore comprise as parameter of the requested quality of service, in particular, the data rate of the datastream and/or its latency, i.e. the maximum transmission time from the sender to the receiver, for example in the form of a requested type of data, apart from possibly still other parameters. The available data rate and/or latency, in particular, will also be called capacity in brief in the context of the invention following.
For the use in a motor vehicle, the new Ethernet AVB standard (IEEE 802.1 BA) is examined with increasing interest which, in contrast to a conventional (normal) standard Ethernet can guarantee a maximum transmission time of data packets (latency). Ethernet AVB data are transmitted as data packets, for example according to IEEE 1722 or the IEEE 1733 transport protocol.
However, before the actual data transmission can begin, a certain quality of service (particularly latency and data rate, also generalized called capacity in the text which follows) is reserved by a reservation request from the sender to one or more receivers, which is forwarded via switches in the communication network if there is no direct link between sender and receiver.
For this purpose, reservation requests are transmitted according to an MSRP (Multiple Stream Reservation Protocol) protocol from the sender, also called talker, to the receiver(s) called listener(s), a maximum of six switches are allowed to be interposed between sender and receiver in order to maintain the latency of the class requested in each case. The network link between two user terminals is called Hop.
Apart from the magnitude of the datastream, the reservation requests usually also contain their transmitting frequency and a so-called AVB class, two classes A and B being provided in accordance with the aforementioned standard. In class A, a maximum transmission time (latency) from the sender to the receiver of 2 ms is guaranteed; these are 50 ms in class B.
When the receiver expects or requests data, it can send out a request to the sender that it wishes to receive a datastream. Like the entire communication between receiver and sender, this request is forwarded to the sender by the switches.
The sender thereupon sends the aforementioned reservation request, which can also be considered as a streaming offer and contains parameters such as the AVB class (also called QoS class—quality of service), the data rate, the rank in the sense of an importance or priority of the message and/or the transmitting frequency. In forwarding the reservation request, the switch checks whether it can still provide these resources in the communication network and, in the case of a positive test, forwards, the message to the receiver or, respectively, in the direction of the receiver to the next switch. The latter responds to the offer and sends back a confirmation.
All switches on the path from the sender to the receiver register the datastream to be transmitted and reserve the necessary quality of service (QoS) via adjustments in their internal queues and registers. If the sender receives a positive return message, the datastream can be transmitted. The datastream is allocated the requested quality of service (QoS). This ensures, inter alia, a defined maximum delay of the datastream during the transmission between the sender and the receiver.
If a reservation cannot be confirmed positively, the sender sending out the reservation request receives a message with a rejection of the reservation request, which usually also contains an error code. Although the error codes provide information about the reason of the rejection which, in a frequent regular case may well be an inadequate capacity, especially an inadequate data rate, they do not provide information about the status of the network for example, the data rate still available.
Thus, there is no possibility of adapting the reservation request selectively to the network to obtain a positive confirmation of the reservation request and to be able to transmit the data speedily in the communication network.
WO 01/82022 A2 discloses an analysis of a network performance in which a number of data packets of a datastream are sent out between network users and an arrival characteristic of each data packet is recorded. By comparing the arrival characteristic of the various data packets, the variability of the data transmission in the network is determined. In these contexts, losses of packets or changes of the transmission time can be investigated, using non-synchronized network users as a basis. However, data rate guarantees cannot be checked by means of this method.
EP 2 247 037 A1 discloses a communication system having a guaranteed data rate in which a data rate reservation request is sent out by an end-point device by interposed switches forwarding the reservation request to the receiver. The switches forward the reservation request in each case in the direction of the terminal if they can meet the data rate request. The reservation request is then sent back by the terminal. This indicates that the data rate reservation is concluded and the data transmission can begin. Otherwise, the data rate reservation request is sent back by the switch which cannot serve the request. This indicates that communication with the requested data rate is not allowed. As an alternative, it is then possible to allow the communication with a reservable data rate or to carry it out as best as possible.
For this purpose, the data rate reservable by the switch is returned as value. With a value of 0, no data rate is reserved and guaranteed but the communication is allowed. The communication is carried out as best as possible. For the method proposed here, however, it is necessary that the switches themselves have considerable logic which makes them expensive and therefore uninteresting for applications in the automobile field. Such a solution is also not compatible with the Ethernet AVB standard.